1. Field of the Invention
The present invention generally relates to file processing units that perform processes such as file open, file close, read, and write, based on accesses made to an external storage device by an application, and, more particularly, to a file processing unit that produces and checks signature information for a designated file.
2. Description of the Related Art
In order to determine whether the data in a file produced utilizing a computer system and stored in an external storage (such as hard disk, optical disk, or floppy disk) has been altered by a third party, signature data is affixed to the file and then checked. Conventionally, such signature data has been produced and checked by means of a special application. More specifically, such signature data is produced and checked in the following manner.
After a file produced by an application is stored in an external storage, a special application designed for producing and checking signature data is started. The file is then read out of the external storage in accordance with the special application, and signature data is produced utilizing all or a part of the data of the read out file. The signature data attached to the corresponding read out file is again stored in the external storage. When the data of the file stored in the external storage in accordance with the special application is to be edited, the special application is started before the file is accessed. In accordance with the special application, the data of the designated file is read out of the external storage, and signature data is produced utilizing all or a part of the data of the designated file. The signature data produced here is then compared with the signature data already attached to the designated file. If both signature data are identical, it is determined that the data in the designated file has not been altered. If the signature data are not identical, it is determined that the data in the designated file has been altered after the older signature data was produced.
Based on the signature data result, a user can determine whether the data of the designated file has been altered. After the determination, the user reads the data of the designated file from the external storage, and performs processes such as editing.
In the conventional system described above, every time a file is processed by an application, it is necessary to start the special application for producing and checking signature data. This makes the signature producing and checking procedure complicated and troublesome.